In the printing industry, lithography is a well-known technique for processing image plates to reproduce an image in the form of oleophilic areas on a hydrophilic surface. When inked with oil-based inks, the oleophilic image areas of the image plate attract ink while the hydrophilic background areas repel ink. The inked image can then be transferred to paper or another permanent medium. In offset lithography, a common method of printing, the printing press image plates are generally attached to rotating drums. Ink on the oleophilic image areas of the image plates is then transferred by contact to a rotating print roller comprising a metal drum or a rubber blanket. Paper carried by a rotating impression roller picks up the inked image as the paper is pressed between the print roller and the impression roller. Using a continuous roll of paper, many thousands of impressions can be made as the paper is fed between the rotating rollers and the image plates are continually re-inked.
Printing press image plates of conventional design are expensive to manufacture, require many process steps for transferring images to the plates, and must be changed to print new images. Because the printing industry loses considerable time and money in changing image plates on printing presses, there has been a long-felt need for an on-press imaging system in which oleophilic image areas can be written rapidly and accurately on erasable, reusable image rollers.